This disclosure relates to sealing holes through which wires pass in electronic devices.
Electronic devices often include walls or partitions through which wires must pass, but which need to be sealed against the passage other materials, mainly air or water. In particular, headphones, and especially active noise-reducing headphones include two, three, or more discrete chambers, each including electronics that must be interconnected, but these chambers need to be acoustically sealed from each other and, at least some of them, from the environment. As shown in FIG. 10, a typical active noise reducing headset 10 has four sections: a front cavity 12 that couples to the user's head 14 with a cushion 16 and contains a feedback microphone 18, a rear cavity 20 that surrounds the back side of an electroacoustic transducer 22 (also called a driver or speaker), a feed-forward microphone cavity 24 that houses a microphone 26 coupled to the environment 28, and an electronics cavity 30 that houses the active noise reduction circuit 32 and power supply 34. There may be more or fewer cavities, depending on the features and architecture of the headphone.
It is particularly important that acoustic paths into and between the front and rear cavities be controlled. The rear cavity 20 contains a specific volume of air, the stiffness of which applied an acoustic impedance to movement of the diaphragm of the transducer 22. As described in U.S. Pat. No. 6,831,984, incorporated here by reference, the rear cavity 20 may be coupled to the environment through precisely designed resistive and reactive ports (not shown). In other examples, the back cavity is entirely sealed. In either case, a hole 40 may be necessary in the cavity wall to allow wires 42 to pass from the transducer 22 to the other electronics 32. In some examples, as shown in FIG. 10, a feed-forward microphone 26 is housed in a recess in the wall of the back cavity. The wires 44 from the microphone to the electronics may pass through a hole 46 in the wall separating the back cavity from the microphone recess, and through another hole 48 in the wall of the back cavity, to the electronics.
The front cavity 12 contains another volume of air, which couples sound from the transducer 22 to the ear canal 50, and it contains the feedback microphone 18, if one is used. Variability of the ear canal 50 and the seal formed between the cushion 16 and the head 14 mean that the volume of the front cavity 12 is not fixed, and leaks may exist between the cushion and the head, but it has been shown that providing another, known and controlled leak path (not shown) that is greater than the typical seal-to-head leak, can allow the headphone design to compensate for some of the variability. As with the back cavity, a hole 52 in the front cavity wall allows wires 54 to pass from the feedback microphone 18 and, in some cases, from the transducer, to the other electronics 32. In some designs, a hole 56 of known size is intentionally provided between the front and back cavities to avoid overpressure situations from damaging the transducer. Again, the specific size of the hole is important to the proper operation of the headphones.
These various wiring holes serve as additional, uncontrolled acoustic leak paths out of the front or back cavity or between them. Similar issues exist in waterproof electronics, where holes must be provided to get wires out of sealed compartments. To avoid such problems, as shown in FIG. 11 for an example headphone 60, the wiring holes are generally sealed with a sealant 62 such as room temperature vulcanizing (RTV) silicone. RTV presents numerous problems in the assembly of headphones. It takes time to cure, sometimes as much as 90 minutes, which delays the total assembly of the product, and causes any rework that requires re-seating the wires to take even more time. RTV also binds the wires, such that they cannot be pulled back through the hole, such as to adjust their length, once it has cured. RTV may also generally be messy to use and clean up. Other sealing techniques, such as expanding foam, are also difficult to work with and may provide inconsistent results. Note that while the use of RTV to seal the holes is prior art as shown in FIG. 11, the actual headphone shown in FIG. 11 is not prior art.